A Light-Emitting Diode (LED), as used herein, is a semiconductor light source for generating a light at a specified wavelength or a range of wavelengths. LEDs are traditionally used for indicator lamps, and are increasingly used for displays. An LED emits light when a voltage is applied across a p-n junction formed by oppositely doping semiconductor compound layers. Different wavelengths of light can be generated using different materials by varying the bandgaps of the semiconductor layers and by fabricating an active layer within the p-n junction.
Traditionally, LEDs are made by growing light-emitting structures on a growth substrate. The light-emitting structures along with the underlying growth substrate are separated into individual LED dies. At some point before or after the separation, electrodes or conductive pads are added to the each of the LED dies to allow the conduction of electricity through the structure. LED dies are then packaged by adding a package substrate, optional phosphor material, and optics such as lens and reflectors to become an optical emitter.
Optical emitter specifications typically identify application-specific radiation patterns outputted by the optical emitter. A commonly used beam pattern is the batwing beam pattern for illuminating a flat surface, in traffic signal applications, or in a backlighting unit for a display. The batwing beam pattern may be defined by having two roughly equal peaks in a candela distribution plot with a valley between the peaks at about 0 degrees.
Optical emitters are designed to meet these specifications. While existing designs of optical emitters have been able to meet batwing beam pattern requirements, they have not been entirely satisfactory in every aspect. Reliable and more efficient designs that are easier to manufacture continue to be sought.